The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Wireless sensor and actor networks (WSANs) refer to a group of sensor nodes and actor nodes wirelessly linked to perform distributed sensing and acting tasks. In one example of WSANs, sensor nodes collect information from their surrounding environment and transmit sensor data to actor nodes, while the actor nodes collaboratively make decisions based on the collected information and take actions upon the environment. WSANs can be applied in various fields, such as space exploration, combat field reconnaissance, border protection, search and rescue, and the like.
Upon their deployment, nodes of WSANs are expected to stay connected with each other and form a network. Network connectivity enables nodes to coordinate their action while performing a task, and to forward their readings, for example, to a base-station that serves as a gateway to remote control centers. However, WSANs are prone to node failures. For example, a node may fail due to an external damage caused by, for example, natural disasters, or because of hardware malfunction, battery depletion or improper initial deployment. In some applications, WSANs operating in a harsh environment may suffer from large scale damage which partitions the network to disjoint segments. For example, in a battle field, parts of the deployment area may be bombed, and nodes in the vicinity would be destroyed and surviving nodes can be split into disjoint partitions (segments). Losing connectivity between partitioned segments prevents data exchange and coordination among some nodes. Therefore, restoring the overall network connectivity is crucial.
The existing solutions for restoring connectivity of partitioned WSANs can be categorized into two categories: self-healing approaches that exploit the existing actor nodes to restore the network connectivity, and relay-based approaches that use external actor nodes in order to restore connectivity.
The self-healing approaches reconnect the separated partitions by reducing the distance between surviving nodes below their transmission range, so it does not require extra node deployment. However, the self-healing approaches require mobility of some nodes, which may increases the cost and adds an extra complexity to the hardware, in addition to high energy consumption for long distance travelling. The self-healing approaches can be subcategorized into centralized approaches and distributed approaches. In centralized approaches, the information about remaining undamaged nodes can be collected possibly by a server which performs the selection of the nodes to move and their final destination, to assure connectivity. The distributed approach does not require complete information about the damage and the partitions.
The relay-based approaches restore connectivity among segments by deployment of additional relay nodes (mobile nodes). Some solutions based on the relay-based approaches may require information about the damaged area, the number of network partitions and the location of the remaining nodes. However, that information may be inaccurate or may not be obtained for some applications where access to the damaged area is impractical due to difficult or dangerous scenarios, such as gas leakage, forest fire, or geographical difficulties (e.g., Amazon forest or active volcanoes). Thus, the relay nodes self-deployment strategies are needed for applications where accurate information of partitioned WSANs is not available.